The present invention relates to the production of camshafts, especially for reciprocating-piston internal combustion engines. More particularly, it relates to a device for holding in orientation, around a tubular shaft, a flat cam of ovoid contour perforated by an orifice through which the said shaft passes, in view of fixation of the cam on the shaft by expanding the said shaft, as well as to a die equipped with a plurality of these devices and to a machine for production of camshafts provided with at least one such die.
From U.S. Pat. Nos. 4,781,076 and 4,858,295, for example, there is already known a process for production of such a camshaft by expanding, wherein the said cams are disposed along a tubular shaft passing through them, after which the said shaft is expanded radially with plastic deformation by forcing an expander tool into the interior thereof in order to fix the said cams on the said shaft. To ensure such fixations, the orifice of the said cams is provided with irregularities of contour, into the hollows of which the peripheral material of the radially expanded shaft penetrates.
The object of the present invention is to provide an advantageous tool for application of such a process.
To this end, the invention relates very particularly to a device for holding in orientation, around a reference axis, a flat cam with ovoid peripheral contour perforated by an orifice through which there can be passed a tubular shaft whose axis then coincides with the said reference axis, in view of fixation of the said cam on the said shaft by expanding this shaft, this device being noteworthy in that it is provided with:
a body provided with a transverse passage for the said shaft and with a conduit for introduction of the said cam, the said introduction conduit opening at one end into the said transverse passage and at the other end at the periphery of the said body;
means for holding the said cam in its introduction conduit in a waiting position in which its orifice is at least approximately coaxial with the said transverse passage;
two first sliding blocks, spaced apart and parallel, interlockingly mounted to move translationally in the said body in a manner that is at least substantially orthogonal to the said transverse passage for the said shaft, the said first sliding blocks being elastically spread apart from the said transverse passage by first elastic means, with their external ends projecting outside the said body on one side thereof and their internal ends disposed facing a part of the ovoid contour of the said cam when this is in the said waiting position;
two second sliding blocks, spaced apart and parallel, in mirror-image relationship to the said first sliding blocks and interlockingly mounted to move translationally in the said body, in a manner that is at least substantially orthogonal to the said transverse passage for the said shaft, the said second sliding blocks being elastically spread apart from the said transverse passage by second elastic means, with their external ends projecting outside the said body on the other side thereof, and their internal ends disposed facing another part of the ovoid contour of the said cam when this is in the said waiting position; and
a mechanical linkage connecting the said first and second sliding blocks such that, when the said first sliding blocks are pressed against the action of the said first elastic means to displace the internal ends of the said first sliding blocks toward the said part of the ovoid contour of the said cam until contact is made therewith, the said second sliding blocks are pressed by the said mechanical linkage against the action of the said second elastic means to displace the internal ends of the said second sliding blocks toward the said other part of the ovoid contour of the said cam until contact is made therewith.
Thus, in the device of the invention, each cam, starting from its waiting position, is pressed in opposing directions by the said first and second sliding blocks, which permits it to be displaced and to turn around its axis so that on the one hand it eliminates the error of its angular position due to the imprecision of introduction into the said conduit by, for example, a robot, and on the other hand it compensates for the errors of precision in production of the said cam. It is therefore easily understood that the said cam is then centered and oriented precisely, regardless of the precision of its production and of how it is oriented relative to the introduction conduit.
Consequently, for a given cam contour and a given angular orientation of the cam, the relative lengths of the said first and second sliding blocks are themselves determined. To be able to adjust these relative lengths and therefore the centering and orientation of each cam, it is advantageous for the said first and second sliding blocks to be adjustable in length. For this purpose they can be provided with a portion of fixed length and a portion of adjustable length comprised, for example, by a set of interchangeable shims of different lengths, with which the angular position of the cam can be adjusted. In addition, to improve the centering and orientation of the cam still further, it is advantageous for the spacing between the said first sliding blocks and the spacing between the said second sliding blocks to be determined as a function of the contour of the cam and of the angular orientation thereof around the said shaft. These spacings are chosen so as to ensure the largest possible lever arm on each sliding block, in order to facilitate orientation while ensuring firm engagement of the said cam by the said first and second sliding blocks in the said waiting position.
In order to facilitate the contact between the contour of the cam on the one hand and the internal ends of the said first and second sliding blocks on the other hand, these sliding blocks are provided with rolling members such as wheels that can roll over the said ovoid peripheral contour.
Advantageously the said means for holding the said cam in waiting position in its introduction conduit comprise a pressing pad pressed elastically toward a position-reference plate interlocked with the said device, the said pressing pad being spread apart elastically from this reference plate during introduction of the said cam flatly between the said pressing pad and the said reference plate. It is seen that the said cam is in this way held by friction while being pressed between the said pressing pad and the said reference plate, and the position of the cam along the said tubular shaft is easily adjustable by disposing thickness shims in front of or behind the said reference plate. Preferably the said means for holding the cam are provided with a stop system against which the said pressing pad is pressed elastically when no cam is in waiting position, this stop system imposing, between the said pressing pad and the said reference plate, a minimum spacing smaller than the thickness of the said cam. In this case in particular, the said pressing pad can be provided with a chamfer on which the said cam, during its displacement toward its waiting position in the said introduction conduit, exerts a pressure that causes the said pressing pad to be spread apart elastically relative to the said reference plate.
In a particularly advantageous embodiment of the device according to the present invention, the said holding means form a mechanical unit inserted and fixed in the said introduction circuit. Thus there can be provided a plurality of different units, each specifically adapted to a particular cam and interchangeable with the other units. Thus the said device can be used for cams of different dimensions and shapes.
To ensure that it can be easily assembled in compact manner with other similar devices, the body of the said device according to the present invention advantageously has the form of a thick plate with parallel faces. For purposes of greater compactness of an assembly of a plurality of such devices, the slideways for the said first and second sliding blocks can be machined in a first of the said parallel faces of the said plate, while the said introduction conduit is machined only partly in this same first face, the second face of the said plate being machined to form partly the introduction conduit of another plate, whose first face can be applied against the said second face of the said plate.
Thus the present invention also relates to a die for production, by expanding, of a tubular camshaft, especially for an internal combustion engine, the said cams being distributed along the said shaft with specific orientations, the said die being provided with as many devices similar to that described as the said shaft has cams, the said devices being assembled one after another in such a way that their transverse passages are aligned to form a channel for the said tubular shaft and in such a way that their cam-introduction conduits are disposed respectively at the position of a cam along the said shaft. In order to ensure that such a die constituted by a succession of such devices having a body in the form of a thick plate corresponds correctly to the positions to be occupied by the said cams along the said shaft, it is possible:
either to determine the thickness of the thick plate constituting the body of each device as a function of the said positions;
or to produce all of the said devices with thick plates of identical thickness and to provide thickness shims designed to be disposed between the said devices.
Such a die can be mounted alone or with at least one identical die on a machine for the production of camshafts by expanding provided with a single actuating member which commonly presses all of the said first sliding blocks of the said die, the actuating member being mounted on the said machine independently of the said die. Thus the control member of the die is interlocked with the machine and not with the die, such that the die can be easily mounted and demounted on the machine, in order, for example, to be replaced by another. It will be noted that such mounting and demounting operations are facilitated by the fact that the die, constituted by a plate assembly, is compact. It is therefore easy to maneuver and can be automatically mounted and demounted on the machine.
To improve the compactness and ease of mounting and demounting of the die even more, it is additionally provided that the stop designed to block one end of the tubular shaft during expansion thereof is also mounted on the said machinexe2x80x94and not on the diexe2x80x94independently of the said die, facing the said channel for the said tubular shaft.
Preferably the machine according to the present invention is equipped with at least two such dies, each able to move from at least one cam-loading station to at least one expanding station then, after discharge of the expanded camshaft, from the said expanding station to the said loading station.
It is therefore seen that, by virtue of the present invention, the expanding machine has numerous advantages:
because it uses cam centering and orienting devices independent from one another and specific to each cam, it has great modularity;
since engagement of each cam by the sliding blocks is symmetric, the precision of centering and orientation of each cam is high regardless of the precision of introduction and production of the said cams;
compactness is ensured by the constitution of the die by devices in the form of plates applied one against the other and assembled together;
interchangeability of the die is easy, since it is compact and does not carry either the expander stop or the sliding-block control member;
adjustments of axial and angular position of the cams can be achieved easily by shims as described hereinabove;
flexibility of the die is high, because it can be used for expanding camshafts of different types using a majority of standard elements and a minimum of elements specific to a particular type of camshaft.